The invention relates to a process for the manufacture of a laminated safety glass pane which in reflected and transmitted light is free from wrinkle-related optical distortions, comprising a first glass pane, a second glass pane and a multi-layer intermediate layer, which intermediate layer in the form of a foil laminate consists of a first laminating foil, a bi-axially stretched thermoplastic carrier foil provided with a thin-film system, and a second laminating foil. The invention furthermore relates to the use of a carrier foil for the manufacture of the laminated safety glass pane as well as to a carrier foil particularly suitable for the process and the use respectively. The laminated safety glass panes may be either flat or curved panes. The flat laminated safety glass panes are used for a great variety of applications, e.g. in the building industry or as side windows of motor vehicles. The term curved laminated safety glass panes denotes, within the framework of the invention, singly curved and, in particular, double curved (spherically bent) laminated safety glass panes, and also so-called complex curved laminated safety glass panes, which at least in some parts have large curvatures, i.e. small radii of curvature. Complex curved laminated safety glass panes are used, in particular, as windscreens or rear windows of motor vehicles.
With the described laminated safety glass panes the thin-film system forms a so-called functional layer. This serves to produce the laminated safety glass panes in such a way that they can fulfil other functions. These functions include, among others, the heatability, the changing of the light and energy transmission degree and reflectance respectively, and the fitting with antennas for the most varying uses. The structure of the thin-film systems and the production thereof are known and proven. Particularly suitable are thin-film systems based on silver layers or semi-conductive metal oxide layers. These thin-film systems are integrated into the laminated safety glass pane with the aid of a transparent thermoplastic carrier. With regard to the state of the art reference is made in so far, for example, to the WO 90/08334, which describes known carrier foils, proven thin-film systems and also customary laminating foils.
Laminated safety glass panes of the type described at the outset often display optical distortions, in particular in reflected light. These optical distortions are caused by phenomena that can be attributed to corrugations in the carrier foils. The optical distortions occur in flat laminated safety glass panes of the described type as well as in curved, especially complex curved laminated safety glass panes.
The known measures from which the invention proceeds (EP 0 077 672) relate to a selectively light-transmitting or electrically conductive film on a carrier foil, which has a thickness between 12 and 125 .mu.m and after a heat treatment at 120.degree. C. for 30 minutes displays a heat shrinkage which depends in a complicated manner on the thickness of the carrier foil. This serves to avoid optical distortions in a laminated safety glass pane, in which the carrier foil is integrated with the thin-film system. Also here the laminated safety glass pane may be flat or curved. Tests have shown that the results that can be obtained according to these teaching are open to criticism. The problems described at the outset, which occur with flat as well as with complex curved laminated safety glass panes, especially in the case of small radii of curvature, are not dealt with.
To prevent that a carrier foil provided with a thin-film system, in particular one of polyethylene terephthalate, which is integrated in a laminated safety glass pane of the type described at the outset, during the manufacture of the laminated safety glass pane changes its properties and as a result thereof causes optical distortions, it is known (EP 0 457 209 A2) to bi-axially stretch the carrier foil at temperatures above the so-called glass temperature, followed by thermo-fixing, and after the thermo-fixing to carry out a further stretching at temperatures below the glass temperature. The measures known in this respect are complicated, the result is unsatisfactory. The problems mentioned at the outset are not dealt with.
The invention is based on the technical problem to indicate simple measures suitable for an industrial series production of the laminated safety glass pane, with which flat as well as curved laminated safety glass panes of the type described at the outset can be manufactured, which do not display optical distortions in reflected and/or transmitted light.
To solve this technical problem, the subject of the invention is the process according to patent claim 1.
The deaeration which belongs to the teachings of the invention is customary and necessary to avoid in the laminated safety glass pane distortions caused by air inclusions. The deaeration must take place effectively and adequately in respect of the laminated safety glass pane as a whole as well as in respect of the foil laminate consisting of laminating foils and carrier foils. The characteristic 1.2) is to be understood as meaning that the laminating technology customary in the manufacture of laminated safety glass is used. The process step according to characteristic 1.1) includes the possibility of producing a pre-laminate of the first laminating foil and the carrier foil as well as, optionally, the second laminating foil. The foils that must be pre-laminated are in this case drawn off, in particular, from stock rolls and joined together using pressure and heat with a simultaneous or prior deaeration, before the pre-laminates produced in this manner are cut to size and placed between the two glass panes.